1. Field Of The Invention
This invention relates to methods of monitoring and photographing vehicles. In a specific embodiment, the invention is directed to a method of accurately photographing a moving vehicle, preferably a vehicle traveling through a traffic intersection. Preferably, the vehicle is photographed in a predetermined zone within the intersection regardless of the speed of the vehicle, its travel pattern, or the length of the vehicle. Preferably, a selected portion of the vehicle is photographed, such as its license plate or tag.
2. Description Of Related Art
Various systems for monitoring traffic in intersections have been proposed, but suffer from one or more shortcomings. Certain devices rely on a predetermined trigger time to take photographs of the vehicle after the vehicle passes over an induction loop in the road. However, in such systems the photograph sometimes xe2x80x9cmissesxe2x80x9d the vehicle if the vehicle is moving either too fast or too slow. Other systems use sensors located at the point where the photograph is taken. U.S. Pat. No. 4,884,072 shows a traffic monitoring device that includes a camera for recording the image of the vehicle in a so-called xe2x80x9cdanger zonexe2x80x9d that corresponds to an induction loop located within the intersection. That device has certain shortcomings, including the need to place the induction loop in the intersection at a point corresponding to the danger zone. Accordingly, the present invention is intended to provide an improved system for monitoring and photographing moving vehicles.
In a broad aspect, this invention relates to methods of monitoring and photographing vehicles. In a specific embodiment, the invention is directed to a method and apparatus for accurately photographing a moving vehicle, preferably a vehicle traveling through a traffic intersection in a predetermined zone within the intersection (xe2x80x9cintersection zonexe2x80x9d). Preferably, the vehicle is accurately and reliably photographed in the intersection zone regardless of the speed of the vehicle, its travel pattern (e.g., whether it hesitates or suddenly accelerates), or the length of the vehicle. Preferably, a selected portion of the vehicle is photographed, such as its rear license plate.
An apparatus of the invention includes a device for triggering a camera to photograph a vehicle within the intersection, where the triggering of the camera is dependent on the speed of the vehicle before entering the intersection and may also be dependent on presence information. The device includes a sensor system (or xe2x80x9csensor arrayxe2x80x9d) to transmit signals corresponding to a moving vehicle and a control system for processing the signals and triggering the camera. The signals preferably include xe2x80x9cposition signalsxe2x80x9d from which a transit time can be calculated, and xe2x80x9cpresence signals,xe2x80x9d from which presence information can be obtained, particularly the location of the rear of the vehicle or the location of the rear wheels of the vehicle. A trigger time for taking a picture of the vehicle may be calculated from the transit time.
The method includes the step of transmitting signals to a control system in response to the vehicle passing over a first traffic sensor and corresponding to the speed of the vehicle. The method may also include the steps of transmitting presence signals to the control system, preferably corresponding to the presence of the vehicle in a known presence zone outside the intersection, and photographing the vehicle in response to those signals. In a specific embodiment of the invention, the triggering of the photograph is dependent on the speed of the vehicle. In another specific embodiment, the triggering of the photograph is dependent on the speed of the vehicle, as well as presence information The system preferably uses a first set of signals (reflecting vehicle speed or transit time) and a second set of signals (reflecting the presence of the vehicle) to determine when to trigger the photograph of the vehicle in the intersection zone.